Bonding
by Soapiepie
Summary: *PREVIOUSLY UPLOADED* Set during CoLS. What if Sebastian had succeeded in making Clary drink from the Infernal Cup? How much will she change? Will she come to accept her brother?
1. Chapter 1

_"Drink," Sebastian said in a vicious whisper, so low she doubted Jace could hear it. "I told you by the end of the night you would do whatever I wanted. _Drink_." His black eyes darkened as he dug the cup in, slicing her bottom lip._

Clary screamed as the dark, vile fluid seeped into the cut and burned its way through her system. She could feel the poison fusing with her own blood, and a violent flood of nausea washed over her. Jace was behind her, supporting her, trying to sooth her with soft words. But it wasn't _her_ Jace, because _her_ Jace wouldn't sit back and watch Sebastian turn her—or anyone else—into a monster. Out of dizziness, as opposed to seeking comfort, Clary sank back against him. Her legs had turned to rubber at the thought that when Sebastian was finished with her, she would be a monster, just like him. Her mind reeled, rejecting the thought. Jace lowered her onto the ground, whispering to her soft words she couldn't comprehend.

Something cold and sharp dug against her numb lips. Sebastian was crouching in front of her, the Infernal Cup pressing against her mouth. He sat on her knees, effectively stopping her legs from moving. Clary jerked her head to the side. "Jace," she tried to say, in her last attempts to bring his real side back. "Jace, you have to stop him! Get him away from us!" She tried wrestling her arms free from his grip, her whole body thrashing violently with the effort. She gave up on Jace and screamed "HELP ME!" in a futile attempt to gain the attention of someone fighting below them. Unfortunately, while her mouth was wide open, Sebastian filled it with the acrid blood, immediately covering his free hand over her mouth and nose, forcing Clary to swallow. She slumped, her energy sapped from her as the poison burned through her system. Her body, still trying to reject the awful, bitter liquid, shut down. Like a giant, aggressive wave, the darkness crashed around Clary as she gave in, defeated, defenceless and alone.

XxXxXxXxXxXxXxXxXxX

At first Clary was conscious of nothing. Then a throbbing, burning pain, like a fire was raging within her. She tried to sit, but a jab of white-hot pain exploded from her chest. She screamed silently, unconsciousness creeping closer, threateningly. Then a cool piece of fabric was placed on her forehead. _Jace?_ She thought, _what happened? Oww, everywhere hurts_.

"Shh. I know it hurts, Clary." The voice was so loud Clary instinctively tried to cover her ears, only to cry out as more pain knifed through her. A stele traced the _iratze_ rune on the inside of her arm, and if it wasn't for the iron grip on her wrist Clary would have jerked away. It wasn't the usual sting, but instead a terrible slow burn which left her whole arm throbbing.

_Sorry, little sis, your senses appear to be extremely sensitive. _Clary gasped, now that the voice wasn't bursting her eardrums, she realised it was lovely; gentle and melodious and…_it was speaking inside her mind!_ "How are you doing that?" She croaked, glad that at least the _iratze_ had somewhat eased her senses. "Wait, you're not Jace…Sebastian?"

_Yours truly. I made a tisane for you which should calm your fever for a while. Here. _His hand slid to the back of her burning head and tilted it slightly. Something cold and sharp dug into Clary's lip and, momentarily ignoring the pain, she jerked away from it, as if there was some traumatic memory she related to the goblet. She moved her head back, embarrassed, and drank obediently. The tisane was smooth and rich and sweet, but slightly bitter, like dark chocolate. Clary found herself eagerly draining the goblet, enjoying the warmth that spread through her. The pain within her receded immediately, and she felt her head clear. "Mmm…what was that?" She asked contently.

Sebastian removed the cup and said, "When you first drank from the Infernal Cup, at the Ceremony, it was not just Great Mother Lilith's blood, but also my own. That has given us, among other things, a telepathic tendency."

She noticed he had failed to answer her question, instead leaving her to do her own deductions. _When I __first__ drank from the infernal cup…was that the goblet I just drank from?_ Sebastian laughed softly, as if he could hear her thoughts. _His blood? __**Was that "tisane" actually his blood? Did I just drink his…?**_But she was distracted from her mental raving when Sebastian slid his cool, calloused fingertips over her cheek, and then stroked her sweat-drenched hair off her face. Clary shivered at his touch, but found herself drawn to it, wanting more.

For a while she was so lost in the light caresses that she almost forgot it was Sebastian doing it. Sebastian her demonic, older brother. Sebastian, who had recently forced _his demon blood_ down her throat. She inhaled sharply, realizing she had completely forgotten about her boyfriend. She directed her thoughts to where she could feel Sebastian sitting on the bed in the darkness next to her. _Jace. Why isn't he here? Where's he?_

She felt him tense._ Easy there, Clary. You are focusing on it too much. Relax a little._

_Like this? _She thought, hesitantly, surprised when she felt him relax again.

"You are a natural at this, my Dear," he said, "I believe we were talking about Jace? There was a slight…complication following the ceremony. The group of Shadowhunters and their Downworlder-scum allies kidnapped him. They tried to get you too, but I would not let them touch you."

_What!?They took Jace!? You mean my family? Did you hurt any of the—_

_"I am your family!" _Sebastian hissed_ "I am the only one who matters!"_

Clary flinched at the abrupt harshness in his voice. She wanted desperately to hear his gentle, lulling voice again. To calm him, she said, "I-I'm sorry, Seb. I didn't mean to offend you. I-I…" She trailed off, suddenly not sure what she was apologizing for. To her relief, he resumed the light stroking that Clary realized she'd begun to love. She shifted her head closer to his fingers and as if sensing her approval, Sebastian made a soft noise.

"The blood had a strange effect on you. I believe it could be because of the abnormal amounts of Angel blood Valentine pumped into you. It was like your system was rejecting it. The fever and pains you are experiencing at the present is an effect of this."

_Am I a monster like you now?_ She whispered inside his mind as the implications of what he had done to her sank in.

"Clarissa, we are not monsters, we are Morgensterns!"he spat, and left.


	2. Chapter 2

Clary woke again, sunlight streaming through her the window and the pain within her palliated, but with an aching feeling something was missing. She eased out of bed to the door, impatient at her immobility. Within her, a nagging sensation motivated her out of the room, down a flight of stairs, through the kitchen and finally, to a closed door. She opened it and stepped inside.

Sebastian looked up from examining a large tome which sat in front of him at a large steel-and-glass desk.

_Seb?_ Clary thought to herself, _he's the thing I was missing?_

"You missed me?" Clary jumped as she felt Sebastian's breath on her neck as he whispered the words into her ears. She marvelled at how stealthily he could move, sneaking up on her like that.

_I still hear your thoughts Clarissa dear, _he said mockingly, and chuckled quietly. His arms slipped around her waist, warm and comforting. She sank into his solid body, the part of her mind that had been nagging her now purring like Chairman Meow did when he was petted.

And for the second time in as many days, Clary yanked away from Sebastian, reprimanding herself for relaxing in his presence. She should be trying to get away from him, not seeking him out. He snarled, as if she had been speaking her thoughts aloud, and before she had time to react, he pounced with cat-like grace and knocked her down. Clary struggled desperately, remembering a similar time just before the ceremony, when he had first violated her personal space uncomfortably. But try as she might, Sebastian had already gotten a hold of her wrists in one of his hands, the other grinding the side of her face into the floorboards. With a razor-sharp claw, he sliced through the sleep-shirt she was wearing, exposing her bare back. Clary whimpered as the hand previously on her head began massaging between her shoulder blades, deceivingly gentle. He worked for a while, rubbing tight circles over the kinks and knots, not ceasing until they were all gone.

Clary hated how skilled his hands were. She hated it, but loved it at the same time, and then hated herself for loving it at all. She could feel herself relenting, calming to his touch, even though she could tell he was about to do something terrible to her and was only comforting her so that his next move wouldn't be expected. And even though she anticipated it, the cool sting of the stele made her jump. Then the weight of Sebastian's body left her, and she scrambled to her feet, backing away from him as fast as her disorientated self could.

"What rune was that?" Clary asked warily.

"I just Marked you as mine, Sister Dear. Not a binding rune; you already have my blood within you. You are now my mate, my queen," he said, almost-reverently, calmly returning to his desk.

"WHAT THE FUCK!? YOU FUCKING ASSHOLE! YOU SICK, TWISTED—" She screamed, collapsing as the most excruciating pain clawed through her body.

"I am your demon sire, and your life-mate. You belong to me now, and you cannot insult me in that way. Let's try again shall we? Come here, Clarissa." His tone left no room for argument, but Clary preferred to be out of his arm's reach. "No," she whispered, noticing the flash of irritation within his onyx eyes. Her satisfaction was short-lived as it was moments later that Clary was returned to the same agony as before.

Finally, the pain receded, and Sebastian, as impassive as ever, said, "You cannot disobey me, Clarissa; you will not be able to. Your inner demon—if you will—won't let you. Come here."

For a split-second, Clary considered stalling again, but her brain easily decided against it. Pitifully, she dragged herself on useless limbs to her captor. When she reached his feet, a blissful, deep pleasure filled every aching crevice of her body.

His voice was suddenly soothing, "But if—and when—you obey me, sweet sister, you reward yourself. That pleasure is no coincidence, Clarissa." Sebastian crouched down and, picking her up off the floor, carried her to her room.

Clary hadn't made her bed when she left it, and Sebastian lay her down and pulled the sheets around her, tucking her in snugly, as if she was a little girl. He turned to leave, but Clary whispered; "Seb, how do I avoid the pain?"

He leant down and kissed her hair, then perched on the edge of her bed. He smoothed her flame-coloured mane, tucking a stray curl behind her ear before saying; "You must learn to be submissive to me, little sister. You must respond to my calls without hesitation. When I say your name, you must cease whatever you are doing, come to me, and give me your undivided attention." His voice slipped into the soft, caressing tone he had used when she was feverous, "You are a clever girl, and as long as you contain that fiery temper, and continue consuming my blood, you will soon find it easy to do my bidding. That is not too demanding of me, is it Clarissa?"

"N-No." Even though her answer was hesitant, he smiled a lovely, charming smile at her answer, kissed her cheek, and straightened. "But Seb?" Clary murmured, realising she _really_ didn't want him to leave. When he turned back around, she asked; "Can you please stay with me, at least until I fall asleep?"

He obliged, and she shuffled over to give him more space. Sebastian wrapped his arms around her possessively, soothing her with whispered soft nothings and feather-light caresses. Worn, she accepted his affection with a new-found tolerance. Having not fully recovered, Clary was already exhausted from her most recent ordeals, but her brain whirred away, not allowing her to sleep. _This link between Sebastian and I is what must be causing the periods of time where I am extremely attracted to him. When I completely forget about Jace, my family, my friends. When I forget that Sebastian is a sick, twisted demon who is holding me prisoner, who has fed me his blood twice now, who just bound me to him and who is my brother for crying out loud! __Not to mention my own disgusting self who, although linked with the freak, sometimes actually likes it!?_

_I really should punish you for thinking those things, Clarissa, but I feel you are starting to trust me. _He grinned, _possibly even like me._

"You say that _after_ I called you all those things?" Clary sighed, "I suppose you can read my mind then?"

_You seemed more self-deprecating._

"You have an ego like the Idris Towers; big, deflecting and indestructible. Don't flatter yourself," Clary quipped, earning a hard-fought grin from her older brother.

_I did strip the wards off Idris recently, little one, you were there. Deflecting?_

"The wards stop mundanes from finding Alicante; likewise you never answer my questions," She said, snuggling closer to him. Sebastian kissed her temple and slipped his fingers onto her navel, his fingertips swirling across the smooth skin there. Clary only just managed to supress the groan which very nearly escaped her lips. "Now you're trying to distract me," Clary gasped. "Wait a second…did you just call me _little one?_"

_If I did? _Sebastian all but purred, and slipped his fingers higher, making Clary shudder.

"S-Stature wise?" Clary asked, failing to stop her voice from quivering too much. She reproached herself for reacting to his touch far too well. "Because then, that is _very not _alright"

He laughed softly, "I suppose your height—or lack of it—" Clary punched his chest, "—is bully-worthy." He sobered astonishingly quickly, his arms tightening around her protectively. "Was there anyone who ever upset you, Clarissa? Let me punish them for you. Let me hurt them, for hurting you."

"Seb. Please don't. It really doesn't matter." Clary gasped as his arms tensed further, squeezing the air from her. _He hurt me. Sebastian made me into a monster, a demon. I don't really know what I am; with copious amounts of angel and demon blood, am I even human anymore? Will he punish himself for me? Huh, doubt it. I don't even know if my friends will accept me or can change me back into a normal person when they come and rescue me. Oh, Jace! Simon! Izzy! Alec! Mum! Luke—_

Sebastian growled, striking her cheek hard, leaving a stinging redness that clashed with her flaming hair. Her body didn't even have the energy to react to it, let alone fight back. Clary hated herself for being so pathetic. She realised she was so wrapped up in Sebastian that she had not even searched the apartment, looked out a window, found a front door or a stele. But she knew why; at least part of her _did not want to leave_, and it bothered her that she didn't mind. Clary knew that her changing had barely started; that her conflicting emotions and thoughts would dissipate with time that the demon inside her would possess her and she would be like Jace when he was bound to Sebastian.

"If you aren't going to rest then make yourself useful. Follow," Sebastian snarled at her. Clary numbly got out of her bed and followed him, regretting she had upset him, longing for the atmosphere of their conversation minutes ago. For a while, Clary was able to forget that there was anything twisted about her relationship with her brother. For a while they were joking, and teasing, and _getting along_.


	3. Chapter 3

Clary followed her brother down the corridor to the room next to his study. With her artist's eye, she studied the way he moved; graceful, lithe and awfully, painfully similar to Jace.

The room was impossibly large for the apartment, with shelves and shelves of books, tomes and scrolls. It also appeared to be multiple storeys high, with ornate, winding staircases leading to balconies, past which Clary couldn't see. She gasped, "This is like that blue box from that show Simon's obsessed with!"

Annoyed, Sebastian ignored her, probably not understanding the reference or bothering to comment snidely on Clary's nerdy best-friend. In the centre of the room was a podium with an old-blood coloured book. Sebastian picked it up and handed it to Clary. The book was leather-bound with thick, yellowed leaves. She flipped through it to find elaborate handwritten script and beautiful, old paintings. The images were all in reds and oranges, depicting destruction and Hell.

"When I am occupied, you will come here and read a text I will have assigned you previously. You can start with this. It is the Book of Revelations, the only useful part of the Christian Bible. You will read this, Clarissa, because it is vital you truly understand our plans, and accept them. When you have finished, you will find me in my study and recite it to me. If you fail to return to my study by an appropriate time, I will come and find you."

Clary opened it to the first page, but couldn't work out what the script said. Then she realised, "This isn't in English!" She shouted at the retreating figure of her older brother. Without turning, he called back, "By the Angel, I always seem to forget how little useful information they teach you mundanes," he sneered. "It is Ancient Greek, sister." _Ancient Greek? That is so unfair! _"I can't even read normal Greek!" Clary yelled. Finally Sebastian looked around at her and said, in an infuriatingly calm voice, "You are in a library, Clarissa. Go figure." The door slammed behind him.

XxXxXxXxXxXxXxXxXxX

Slightly less than an hour later, the door opened. Without looking up, Clary, in tears of frustration, shouted, "An hour is a really 'appropriate time' for anyone to learn a whole extinct language and read a book!"

"Pardon me, Mistress," a raspy, toneless voice croaked. Clary shrieked, expecting Sebastian's drawl. A rigid Amatis Herondale stood at the open door, wearing simple black work pants and shirt, holding a delicate tea set balanced on a silver tray. Clary sobbed when she saw Luke's sister.

_**Jonathan Christopher Morgenstern!**_ She screamed in his mind, _**Sebastian, that is sick! That is low, even for you! Why would you make her serve me?**_

_Fuck, Clarissa! My brain is vibrating in my head!_

_**As if you can feel anything, you monster!**_

_Can you please calm down? By the Angel, Clarissa, just tell Amatis to leave!_

_**I'll kill you for that! How dare you defile Amatis Herondale's name! Was killing her and replacing her with this demon thing not enough for you? How could I ever love you, when you can't even feel a damn thing!? I could never love a monster like you! I hate yo— **_Clary screamed as pain slashed through her body, shredding her insides, dizziness and nausea like machine-gun ammunition, tearing at her. She waited for it to finish, but the wave did not end; just went on and on, every second, a decade, every decade, infinity.

Finally, Clary collapsed, her body battered, cracked, broken. Darkness crashed around her like curtains signalling the end of a play.


End file.
